1. Technical Field
This disclosure relates to a stress-distribution detecting semiconductor package group used to detect stress distribution in a resin-encapsulated semiconductor package, and also relates to a detection method of stress distribution in a semiconductor package (hereinafter, referred to as “semiconductor-package stress-distribution detection method”) using the stress-distribution detecting semiconductor package group.
2. Description of the Related Art
With the recent rapid growth in popularity of portable electronic devices, there is a demand for reducing the size of electronics used in such portable electronic devices, and ICs (Integrated Circuits) are no exception. The demand has increased not only for size reduction but also for high accuracy, and increasing the initial accuracy of analog ICs and minimizing the property variations, for example, are major technical challenges for device development.
One factor that impedes producing ICs having highly accurate electrical properties is property change in a semiconductor device associated with a molded package process. A property change occurs as a molding resin having a high linear expansion coefficient hardens and contracts in a resin encapsulation process, which causes compressive stress over the surface of the semiconductor chip. For various devices, the piezoelectric effect due to this compressive stress causes change in their electrical properties, which then results in changing their circuit characteristics having been obtained at wafer level. SPICE parameters extracted from wafer-level measurements are generally used in circuit designing, and therefore the property change caused by the molded packaging is not taken into account in the design.
In trying to address such a problem, there is a disclosed method of employing a stress-distribution detecting semiconductor chip, on which multiple piezoelectric resistive elements are formed, and detecting distribution of stress applied to the stress-distribution detecting semiconductor chip due to resin encapsulation molding (for example, see Patent Document 1). Since the resistance of a piezoelectric resistive element changes with stress, the distribution of stress applied to the stress-distribution detecting semiconductor chip can be detected by measuring change in the resistance of each piezoelectric resistive element from before to after resin encapsulation.    Patent Document 1: Japanese Laid-open Patent Application Publication No. 2005-209827
In a stress-distribution detecting semiconductor chip, both terminals of each piezoelectric resistive element are respectively connected to different electrode pads to measure the resistance of the piezoelectric resistive element. In order to accurately reflect the stress distribution detected using the stress-distribution detecting semiconductor chip in the designing process of a finished product of a semiconductor chip, not only the packaging structure but also the chip size and the number of electrode pads need to be made the same between the stress-distribution detecting semiconductor chip and the finished semiconductor chip.
However, if an equal number of electrode pads are provided for the finished semiconductor chip and for the stress-distribution detecting semiconductor chip, the number of piezoelectric resistive elements on the stress-distribution detecting semiconductor chip is limited by the number of electrode pads of the finished semiconductor chip, and accordingly a conventional stress-distribution detecting semiconductor chip is not able to thoroughly detect the stress distribution over the entire, extent of the semiconductor chip. For example, in the case of a small IC of less than 1 mm in size, about four to eight electrode pads are provided; however, only two to four stress-detection piezoelectric resistive elements can be disposed on a stress-distribution detecting semiconductor chip for such a small IC. That is to say, change in the resistance of the piezoelectric resistive elements can be measured at only two to four positions on the stress-distribution detecting semiconductor chip, thus leaving a problem of not being able to thoroughly detect the stress distribution over the entire extent of the semiconductor chip.